Method and device for detecting three-dimensional information

ABSTRACT

An image of an object illuminated by illumination light having given intensity is formed as an optical image. The distance between respective points of the object is determined on the basis of a video which is obtained by acquiring the optical image with a given image pick-up gain. Here, either the intensity of the illumination light or the image pick-up gain is changed with time. The distribution of intensity of the image acquired by utilization of such intensity or image pick-up gain reflects a time lag between the time at which the illumination light is emitted from a light source and the time at which the light reflected from individual points of the object reaches an image pick-up device. The distribution of intensity includes information pertaining to the distance between the light source and the respective points of the object.

CROSS REFERENCE

This is a divisional application of U.S. application Ser. No.09/418,441, filed Oct. 15, 1999, now U.S. Pat. No. 7,016,519 thedisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for detectingthree-dimensional information pertaining to an object which can beapplied to acquisition of a three-dimensional image, and moreparticularly, to a method and device which detects three-dimensionalinformation pertaining to an object by two-dimensionally measuring thedistance between points of the object at a speed at which thethree-dimensional information can be followed in real time within aperiod relating to a frame of a video signal (hereinafter referred tosimply as a “frame period”).

PRIOR ART

The following methods have conventionally been employed as techniquesfor measuring the distance between an object and an image acquisitiondevice or three-dimensional information through use of light.

(1) As shown in FIG. 12, a pulse laser beam or a laser beam whoseamplitude is modulated by a sinusoidal wave is radiated onto an object,and the distance between the object and the laser is measured on thebasis of a period of time during which reflected light returns to thelaser or a modulated phase of the reflected light.

(2) As shown in FIG. 13, under the method (1), the distance between therespective points of an object is two-dimensionally measured bytwo-dimensionally scanning the laser beam over the object.

(3) As shown in FIG. 14, illumination light is modulated by a sinusoidalsignal, and a light amplification gain of an image intensifier disposedin front of an image pick-up element is modulated through use of thesinusoidal signal. An optical image formed by collecting light reflectedfrom the object through use of a lens includes a modulated phasecorresponding to the distance between the object and the lens. Of anoptical image input to the image intensifier, only a portion of theimage whose phase matches a change in the light amplification gain isemphasized. As a result, the points of the object equidistantly spacedaway from the lens can be two-dimensionally captured in the form ofcontour lines. The principle behind the third method is described indetail in Japanese Patent Application Laid-Open No. Hei-6-294868entitled “Imaging Laser Radar Device.”

PROBLEM TO BE SOLVED BY THE INVENTION

According to the method described in connection with (1), the distancebetween a single point of the object and the laser is measured, andhence three-dimensional information pertaining to the object cannot beproduced. In order to acquire three-dimensional information by measuringtwo-dimensional distribution of the distance among the respective pointsof the object, the light beam must be moved so as to two-dimensionallyscan the object as mentioned in the method (2). Alternatively, accordingto method (3), since only portions of the object equidistantly spacedaway from the lens are extracted, the modulated phase of illuminationlight must be changed to only a required extent in order to acquirethree-dimensional information pertaining to the entirety of the object.Methods (2) and (3) require two-dimensional raster-scanning of anillumination light beam and a change in the modulated phase of theillumination light. Therefore, under these methods, acquiringthree-dimensional information pertaining to the object at a speed equalto the frame period of a video signal is difficult. Therefore, themethods are not suitable for acquiring a three-dimensional image.

The object of the present invention is to provide a method and devicewhich solve the problem of the conventional technique, are suitable foracquiring a three-dimensional image, and enable detection ofthree-dimensional information pertaining to an object within a period oftime corresponding to the frame of a video signal.

SUMMARY

A three-dimensional information detecting method of the presentinvention comprises steps of: forming an image of an object illuminatedby illumination of the modulated light having given intensity as anoptical image, and detecting the distance between individual points ofthe object on the basis of an image obtained by acquisition of theoptical image with a given image pick-up gain. Under this method, eitherthe given intensity or the image pick-up gain is changed with time, andthe distance between respective points of the object can be detected ata speed at which the three-dimensional information can be followed realtime within a period of time corresponding to the frame of a videosignal. By utilization of the intensity or image pick-up gain which ischanged with time, the two-dimensional distribution of intensity oflight including information pertaining to the distance between therespective points of the object is acquired. Accordingly, the distancebetween respective points of the object can be determined on the basisof the intensity level information, whereby three-dimensionalinformation pertaining to the object can be detected.

The image of the object can be acquired a plurality of times within theperiod of time corresponding to one frame of the video signal. In such acase, a signal-to-noise ratio (S/N) is improved by means of the storageeffect of the image pick-up element, and the image pick-up intensity isenhanced.

A device for detecting three-dimensional information of the presentinvention comprises a projection section capable of projectingillumination light having given intensity on an object; an image pick-upsection capable of acquiring an image of the object with a given imagepick-up gain; and a signal processing section which calculates thedistance between respective points of the object on the basis ofintensity level information included in a video signal output from theimage pick-up section. Either the given intensity or the image pick-upgain is changed with time, and the distance between respective points ofthe object can be detected at a speed at which the three-dimensionalinformation can be followed real time within a period of timecorresponding to the frame of a video signal. By utilization of theintensity or image pick-up gain which is changed with time, thetwo-dimensional distribution of intensity of the image of the objectthat is acquired by the image pick-up section includes informationpertaining to the distance between the respective points of the object.Accordingly, the signal processing section can calculate the distancebetween respective points of the object on the basis of the intensitylevel information. The device can acquire an image of the object withina sufficiently short period of time. So long as the signal processingsection can compute the distance between respective points of the objectat sufficient speed, the distance between respective points of theobject can be detected at a speed at which the three-dimensionalinformation can be followed within a period of time corresponding to theframe of a video signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of athree-dimensional information detecting device according to a firstembodiment of the present invention;

FIG. 2 is an illustration for describing a method of detectingthree-dimensional information by utilization of illumination light whichlinearly increases and has given intensity and a pulse-like imagepick-up gain in combination, wherein FIG. 2A shows a time-varyingwaveform determined by the intensity I of illumination light and animage pick-up gain “g,” and FIG. 2B shows a time-varying waveformdetermined by the image pick-up gain “g” and the intensity I_(R) oflight reflected from an object spaced away from a projection section byonly distance “d”;

FIG. 3 is an illustration for describing a method of detectingthree-dimensional information by utilization of illumination light whichlinearly decreases and has given intensity and a pulse-like imagepick-up gain in combination, wherein FIG. 3A shows a time-varyingwaveform determined by the intensity I of illumination light and animage pick-up gain “g,” and FIG. 3B shows a time-varying waveformdetermined by the image pick-up gain “g” and the intensity I_(R) oflight reflected from an object spaced away from a projection section byonly distance “d”;

FIG. 4 is an illustration for describing a method of detectingthree-dimensional information by utilization of illumination light whichlinearly increases and decreases and has given intensity and apulse-like image pick-up gain in combination, wherein FIG. 4A shows atime-varying waveform determined by the intensity I of illuminationlight and an image pick-up gain “g,” and FIG. 4B shows a time-varyingwaveform determined by the image pick-up gain “g” and the intensityI_(R) of light reflected from an object spaced away from a projectionsection by only distance “d”;

FIG. 5 is an illustration for describing a method of detectingthree-dimensional information by utilization of a given image pick-upgain which linearly increases and illumination light having pulse-likeintensity in combination, wherein FIG. 5A shows a time-varying waveformdetermined by the intensity I of illumination light and an image pick-upgain “g,” and FIG. 5B shows a time-varying waveform determined by theimage pick-up gain “g” and the intensity I_(R) of light reflected froman object spaced away from a projection section by only distance “d”;

FIG. 6 is an illustration for describing a method of detectingthree-dimensional information by utilization of a given image pick-upgain which linearly decreases and illumination light having a pulse-likeintensity in combination, wherein FIG. 6A shows a time-varying waveformdetermined by the intensity I of illumination light and an image pick-upgain “g,” and FIG. 6B shows a time-varying waveform determined by theimage pick-up gain “g” and the intensity I_(R) of light reflected froman object spaced away from a projection section by only distance “d”;

FIG. 7 is an illustration for describing a method of detectingthree-dimensional information by utilization of a given image pick-upgain which linearly increases and decreases and illumination lighthaving pulse-like intensity in combination, wherein FIG. 7A shows atime-varying waveform determined by the intensity I of illuminationlight and an image pick-up gain “g,” and FIG. 7B shows a time-varyingwaveform determined by the image pick-up gain “g” and the intensityI_(R) of light reflected from an object spaced away from a projectionsection by only distance “d”;

FIG. 8 is a schematic diagram showing the configuration of a projectionsection equipped with a light-emitting element whose light is directlymodulated;

FIG. 9 is a schematic diagram showing the configuration of a projectionsection equipped with a light-emitting element whose light is indirectlymodulated;

FIG. 10 is an illustration showing the configuration of an image pick-upsection employing an image intensifier (II) with gating operation;

FIG. 11 is an illustration showing the configuration of a signalprocessing section;

FIG. 12 is an illustration showing a conventional method of measuringthe distance between an object and a three-dimensional informationdetecting device on the basis of a lag time or modulated phase of areflected laser beam;

FIG. 13 is an illustration showing a conventional method of activating alaser beam so as to effect two-dimensional scanning; and

FIG. 14 is an illustration showing the configuration of a conventionalimaging laser radar apparatus.

DESCRIPTION OF THE REFERENCE NUMERALS

1 . . . signal generation section, 4 . . . lens, 5 . . . imageintensifier with gating operation, 6 . . . image pick-up element, 7 . .. signal processing section, 10 . . . projection section, 11 . . . imagepick-up section, 20 . . . optical image transfer optical system, 21 . .. gate, 22 . . . image split circuit, 30 . . . illumination opticalsystem, 31 . . . light-emitting element, 32 . . . external modulator

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Various embodiments of the present invention will be describedhereinbelow by reference to the accompanying drawings. FIG. 1 is aschematic diagram showing a three-dimensional information detectingdevice according to a first embodiment of the present invention. Thedevice comprises a projection section 10 capable of illuminating anobject with illumination light S6 whose amplitude is modulated; an imagepick-up section 11 which receives light S7 reflected from the objectwhile changing an image pick-up gain with time and captures an opticalimage of the object; a signal processing section 7 for converting videosignals S41 and S42 output from the image pick-up section 11 into athree-dimensional information signal S5; and a signal generation section1 which produces an illumination light modulation signal S1, an imagepick-up modulation signal S2, and a control signal S3. The specificconfiguration of these constituent elements will be described later.

The principle behind the three-dimensional information detecting methodof the present invention which uses the device shown in FIG. 1 will bedescribed by reference to a specific example in which the intensity ofthe light source or an image pick-up gain is linearly changed with time.

The three-dimensional information detecting method according to a firstembodiment of the present invention will be described by reference toFIGS. 2 and 3. As shown in FIG. 2A, the intensity I of illuminationlight is subjected to amplitude modulation, to thereby obtain I=St,where “t” represents time and “S” represents the rate of increase inintensity (=2I₀/T). As shown in FIG. 2B, the intensity I_(R) of lightreflected from the object which is spaced by only distance “d” away froman exit of the projection section 10 is changed, as specified byS(t−2d/v), with a delay equal to a duration of time during which lighttravels between the projection section and the object (=2d/v, where “v”represents light speed). If reflected light having intensity I₊ atcertain time t=t₀ is acquired for only a short period of time Δt (<<T)while an image pick-up gain “g” is taken as g=g₀ (>0), the intensity I₊of the resultant image is expressed by Equation (1).

$\begin{matrix}{{I_{+}g_{0}} = {\frac{\sigma}{\left( {4\;\pi\; d^{2}} \right)^{2}}g_{0}{S\left( {t_{0} - {2{d/\upsilon}}} \right)}}} & (1)\end{matrix}$where σ represents the area of the backward scattering cross-section ofan object. Equation (1) includes information pertaining to the distancebetween the object and the three-dimensional information detectingdevice. In order to eliminate the dependency of term σ/(4πd²)², thesecond image of the object is acquired while the intensity I ofillumination light is uniformly maintained at I=I_(r) for a short periodof time Δt from time T′. At this time, luminous intensity I_(ref)g₀ isexpressed by Equation (2).

$\begin{matrix}{{I_{ref}g_{0}} = {\frac{\sigma}{\left( {4\;\pi\; d^{2}} \right)^{2}}g_{0}I_{r}}} & (2)\end{matrix}$The following equation is derived from Equations (1) and (2).

$\begin{matrix}{R_{+} = {\frac{I_{+}g_{0}}{I_{ref}g_{0}} = \frac{S\left( {t_{0} - {2{d/\upsilon}}} \right)}{I_{r}}}} & (3)\end{matrix}$From Equation (3), we have

$\begin{matrix}{d = {\frac{1}{2}{{\upsilon\left( {t_{0} - {\frac{I_{r}}{S}R_{+}}} \right)}.}}} & (4)\end{matrix}$Further, let I_(r)=I₀; then

$\begin{matrix}{d = {\frac{1}{2}{{\upsilon\left( {t_{0} - {\frac{T}{2}R_{+}}} \right)}.}}} & (5)\end{matrix}$From Equation (4) or (5), we have distance “d.”

As mentioned above, the intensity of respective points of an opticalimage formed by collection of the light reflected from the objectexposed to amplitude-modulated light includes information pertaining tothe distance between the three-dimensional information detecting deviceand a corresponding point of the object. So long as the object iscaptured in the manner as mentioned above and Equation (4) or (5) isapplied to the intensity of each of the pixels of the image, informationpertaining to the distance between the respective points of the objectare two-dimensionally obtained, whereby three-dimensional informationpertaining to the object can be detected.

As shown in FIGS. 3A and 3B, even when the intensity I of the lightsource diminishes, as specified by I=I₀−St, the distance “d” can beobtained in the same manner as mentioned previously.

$\begin{matrix}{{I_{-}g_{0}} = {\frac{\sigma}{\left( {4\;\pi\; d^{2}} \right)^{2}}g_{0}\left\{ {I_{0} - {S\left( {t_{0} - {2{d/\upsilon}}} \right)}} \right\}}} & (6) \\{R_{-} = {\frac{I_{-}g_{0}}{I_{ref}g_{0}} = \frac{I_{0} - {S^{\prime}\left( {t_{0} - {2{d/\upsilon}}} \right)}}{I_{r}}}} & (7) \\{d = {\frac{1}{2}{\upsilon\left( {t_{0} - \frac{I_{0} - {I_{r}R_{-}}}{S}} \right)}}} & (8)\end{matrix}$Further, let I_(r)=I₀; then

$\begin{matrix}{d = {\frac{1}{2}\upsilon{\left\{ {t_{0} - {\frac{T}{2}\left( {1 - R_{-}} \right)}} \right\}.}}} & (9)\end{matrix}$As in the case of the previous example, the optical image formed bycollection of light reflected from the object. So long as Equation (8)or (9) is applied to each of the pixels of the image, informationpertaining to the distance between the respective points of the objectare two-dimensionally obtained, whereby three-dimensional informationpertaining to the object can be obtained.

Referring to FIG. 4, a three-dimensional information detecting methodaccording to a second embodiment of the present invention will now bedescribed. As shown in FIG. 4, the object is illuminated while theintensity of illumination light is modulated by employment of atriangular waveform. An optical image of reflected light is acquiredtwice; in other words, an optical image of reflected light whoseintensity is I₊ is acquired at time t=t₀ for only a short period of timeΔt (<<T) with an image pick-up gain g=g₀(>0), and an optical image ofreflected light whose intensity is I⁻ is acquired at time t=to+T/2 foronly a short period of time Δt (<<T) with the image pick-up gaing=g₀(>0). From Equations (1) and (6), we have

$\begin{matrix}{R = {\frac{I_{+}g_{0}}{I_{-}g_{0}} = \frac{S\left( {t_{0} - {2{d/\upsilon}}} \right)}{I_{0} - {S\left( {t_{0} - {2{d/\upsilon}}} \right)}}}} & (10) \\{d = {\frac{1}{2}\upsilon{\left\{ {t_{0} - {\frac{I_{0}}{S}\left( \frac{R}{1 + R} \right)}} \right\}.}}} & (11)\end{matrix}$Let the wavelength of illumination light modulated by a triangularwaveform be defined as λ=νT; then from S=I₀/(T/2), we have

$\begin{matrix}{d = {{\frac{1}{2}\upsilon\; t_{0}} - {\frac{\lambda}{4}{\left( \frac{R}{1 + R} \right).}}}} & (12)\end{matrix}$Further, if t₀ is set to a given value, distance “d” can be expressed asa relative distance with reference to a reference point d_(ref).Equation (13) represents a relative distance with reference to d_(ref)=0when t₀=T/4.

$\begin{matrix}{d = {\frac{\lambda}{8}\left( \frac{1 - R}{1 + R} \right)}} & (13)\end{matrix}$As in the case of the first embodiment, the optical image is formed bycollection of light reflected from the object. So long as any one ofEquations (11), (12), and (13) is applied to each of the pixels of theimage, information pertaining to the distance between the respectivepoints of the object are two-dimensionally obtained, wherebythree-dimensional information pertaining to the object can be obtained.

According to a method which is complementary to the three-dimensionalinformation detecting methods described in connection with the first andsecond embodiments, three-dimensional information pertaining to anobject can be detected by capturing the image of the object with animage pick-up gain, which linearly increases or decreases, through useof illumination light modulated in the form of a pulse for a shortperiod of time.

A three-dimensional information detecting method according to a thirdembodiment of the present invention will be described by reference toFIGS. 5 and 6. As shown in FIG. 5A, illumination light is modulated suchthat an image pick-up gain “g” is linearly increased (i.e., g=Ut).Further, an object is exposed to light which illuminates like a pulsewith intensity I=I₀ for only a short period of time Δt (<<T). Here, Udesignates the rate of increase in image pick-up sensitivity (=2g₀/T).The image pick-up gain g₊ obtained when the light reflected from theobject that is spaced only distance “d” from the three-dimensionalinformation detecting device has returned to the image pick-up devicebecomes g₊=U(t₀+2d/v). The intensity I_(rO)g₊ of an image resulting fromthe reflected light being captured is expressed by Equation (14).

$\begin{matrix}{{I_{r\; 0}g_{+}} = {\frac{\sigma}{\left( {4\;\pi\; d^{2}} \right)^{2}}I_{0}{U\left( {t_{0} + {2{d/\upsilon}}} \right)}}} & (14)\end{matrix}$Further, in order to eliminate the dependency of term σ/(4πd²)², theobject is illuminated for a short period of time Δt from time T′ whilethe image pick-up gain “g” is uniformly maintained at g=g_(r). At thistime, luminous intensity I_(r0)g_(r) is expressed by Equation (15).

$\begin{matrix}{{I_{r\; 0}g_{r}} = {\frac{\sigma}{\left( {4\;\pi\; d^{2}} \right)^{2}}I_{0}g_{r}}} & (15)\end{matrix}$The following equation is derived from Equations (14) and (15).

$\begin{matrix}{R_{+} = {\frac{I_{r\; 0}g_{+}}{I_{r\; 0}g_{r}} = \frac{U\left( {t_{0} + {2{d/\upsilon}}} \right)}{g_{r}}}} & (16)\end{matrix}$From Equation (16), we have

$\begin{matrix}{d = {\frac{1}{2}{\upsilon\left( {{- t_{0}} + {\frac{g_{r}}{U}R_{+}}} \right)}}} & (17)\end{matrix}$Further, suppose g_(r)=g₀; the following expression is derived fromU=g₀/(T/2).

$\begin{matrix}{d = {\frac{1}{2}{\upsilon\left( {{- t_{0}} + {\frac{T}{2}R_{+}}} \right)}}} & (18)\end{matrix}$The distance “d” is derived from Equation (17) or (18). As in the caseof the first and second embodiments, an optical image formed bycollection of the light reflected from the object is captured. So longas Equation (17) or (18) is applied to the intensity of each of thepixels of the image, information pertaining to the distance between therespective points of the object are two-dimensionally obtained, wherebythree-dimensional information pertaining to the object can be detected.

As shown in FIG. 6A, even when the image pick-up gain “g” decreases(g=g₀−Ut), the distance “d” can be obtained in the same manner as thatemployed previously.

$\begin{matrix}{{I_{ro}g_{-}} = {\frac{\sigma}{\left( {4\;\pi\; d^{2}} \right)^{2}}I_{0}\left\{ {g_{0} - {U\left( {t_{0} + {2{d/\upsilon}}} \right)}} \right\}}} & (19) \\{R_{-} = {\frac{I_{ro}g_{-}}{I_{ro}g_{r}} = \frac{g_{0} - {U\left( {t_{0} + {2{d/\upsilon}}} \right)}}{g_{r}}}} & (20) \\{d = {\frac{1}{2}{\upsilon\left( {{- t_{0}} + \frac{g_{0} - {R_{-}g_{r}}}{U}} \right)}}} & (21)\end{matrix}$Further, let g_(r)=g₀; then

$\begin{matrix}{d = {\frac{1}{2}\upsilon\left\{ {{- t_{0}} + {\frac{T}{2}\left( {1 - R_{-}} \right)}} \right\}}} & (22)\end{matrix}$As mentioned previously, an optical image formed by collection of thelight reflected from the object is captured. So long as Equation (21) or(22) is applied to the intensity of each of the pixels of the image,information pertaining to the distance between the respective points ofthe object are two-dimensionally obtained, whereby three-dimensionalinformation pertaining to the object can be detected.

A three-dimensional information detecting method according to a fourthembodiment of the present invention will now be described by referenceto FIGS. 7A and 7B. As shown in FIG. 7A, the image pick-up gain “g” ismodulated through use of a triangular waveform, and an object isilluminated twice; in other words, an optical image is illuminated attime t=t₀ through use of light which illuminates in a pulsating mannerwith intensity I=I₀ for only a period of time Δt (<<T), and an object isilluminated at time t=t₀+T/2 through use of light which illuminates in apulsating manner with intensity I=I₀ for only a period of time Δt (<<T).From Equations (15) and (19), we have

$\begin{matrix}{R = {\frac{I_{ro}g_{+}}{I_{ro}g_{-}} = \frac{U\left( {t_{0} + {2{d/\upsilon}}} \right)}{g_{0} - {U\left( {t_{0} + {2{d/\upsilon}}} \right)}}}} & (23) \\{d = {\frac{1}{2}\upsilon\left\{ {{- t_{0}} - {\frac{g_{0}}{U}\left( \frac{R}{1 + R} \right)}} \right\}}} & (24)\end{matrix}$Suppose the wavelength of the triangular waveform used for modulatingthe image pick-up sensitivity is defined as λ=νT for convenience's sake,the following expression is derived from U=g₀/(T/2).

$\begin{matrix}{d = {{{- \frac{1}{2}}\upsilon\; t_{0}} - {\frac{\lambda}{4}\left( \frac{R}{1 + R} \right)}}} & (25)\end{matrix}$As in the case of the second embodiment, if t₀ is set to a given value,the distance “d” can be expressed as a relative distance with referenceto the reference point d_(ref). Equation (26) represents the relativedistance with reference to d_(ref)=0 when t₀=T/4.

$\begin{matrix}{d = {{- \frac{\lambda}{8}}\left( \frac{1 - R}{1 + R} \right)}} & (26)\end{matrix}$As mentioned previously, an optical image formed by collection of thelight reflected from the object is captured. So long as Equation (24),(25), or (26) is applied to each of the pixels of the image, informationpertaining to the distance between the three-dimensional informationdetecting device and the respective points of the object aretwo-dimensionally obtained, whereby three-dimensional informationpertaining to the object can be detected.

A method of increasing the image pick-up sensitivity in each of theprevious embodiments will now be described. In the previouslyembodiments, acquisition of an image having intensity I₊g₀ and an imagehaving intensity I_(ref)g₀ for the purpose of determining R₊,acquisition of an image having intensity I⁻g⁻ and an image havingintensity I_(ref)g₀ for the purpose of obtaining R⁻, or acquisition ofan image having intensity I₊g₀ and an image having intensity I⁻g₀ forthe purpose of determining R is performed a plurality of times withinthe period of time corresponding to one frame of an image signal. As aresult, the signal-to-noise ratio (SIN) is improved by the storageeffect of the image pick-up element used for acquiring an image, wherebythe image pick-up sensitivity is improved.

The configuration of the three-dimensional information detecting deviceshown in FIG. 1 will now be described in detail by reference to thedrawings.

FIG. 8 shows a projection section 10 a which is another embodiment ofthe projection section 10 shown in FIG. 1. The projection section 10 acomprises a light-emitting element 31 whose light can be directlymodulated by an illumination modulation signal S1, and an illuminationoptical system 30 which is disposed opposite the light exit surface ofthe light-emitting element 31, which shapes the light emitted from thelight-emitting element 31, and which directs the light toward theobject. For example, a semiconductor laser diode or a semiconductorlight-emitting diode can be employed as the light-emitting element 31.When such a light-emitting element is activated directly by theillumination light modulation signal S1 which is an electric signal, theelement can emanate light whose intensity is changed at high speed. Thethus produced light is shaped by means of an illumination optical system30 so as to illuminate an object, whereby illumination light S6 isproduced. Accordingly, illumination light whose intensity is arbitrarilychanged at high speed, such as increment light, decrement light, orpulse-like light, can be realized by means of the illumination lightmodulation signal S1. As mentioned above, the projection section havingthe configuration shown in FIG. 8 can be used as means for controllingthe intensity of illumination light under the three-dimensionalinformation detecting method of the present invention.

FIG. 9 shows a projection section 10 b which is still another embodimentof the projection section 10 shown in FIG. 1. The projection section 10b comprises a light-emitting element 33 which outputs given light; anexternal modulator 32 which is disposed opposite the light exit surfaceof the light-emitting element 33 and indirectly modulates the lightemanated from the light-emitting element 33 in accordance with theillumination light modulation signal S1; and an illumination opticalsystem 30 which shapes the light output from the external modulator 32and is directed toward the object. An electro-optical effect lightmodulator or an electro-acoustic effect modulator can be used as theexternal modulator 32. Light whose intensity is modulated arbitrarilyand at high speed can be produced by indirect modulation of the givenlight 34 output from the light-emitting element 34, through use of theexternal modulator 32. The thus-produced light is shaped by theillumination optical system 30 so as to illuminate an object, wherebythe illumination light S6 is produced. Like the projection section shownin FIG. 8, the projection section whose configuration is show in FIG. 9can be used as means for controlling the intensity of illumination lightunder the three-dimensional information detecting method of the presentinvention.

FIG. 10 shows an image pick-up section 11 which is another embodiment ofthe image pick-up section 11 shown in FIG. 1. The image pick-up section11 comprises a lens 4 which receives light reflected from an object andproduces an optical image, an image pick-up element 6 which is disposedbehind the lens 4 and picks up the optical image output from the lens 4,and an image split circuit 22 which outputs a video signal pertaining toa plurality of screens included in the electric signal output from theimage pick-up element 6 while the video signal is divided intorespective screens. Further, an image intensifier with gating operation5 capable of controlling the image pick-up gain in accordance with theimage pick-up gain modulation signal S2, which is an electric signal, isattached to the front surface of the image pick-up element 6 via anoptical image transfer optical system 20. A fiber plate or lens can beused as the optical image transfer optical system 20. Light S7 reflectedfrom an object is formed on a photo-electric screen of the imageintensifier with gating operation 5 by means of the lens 4. An opticalimage amplified by the image intensifier with gating operation 5 istransferred by the optical image transfer optical system 20 and input tothe photo-electric screen of the image pick-up element 6.

The light amplification gain of the image intensifier with gatingoperation 5 can be controlled at high speed by means of a voltage to beapplied to a gate 21 of the image intensifier with gating operation 5.In the image pick-up section 11, the image pick-up gain can be changedat high speed by application of the image pick-up gain modulation signalS2 to the gate 21. Accordingly, an image pick-up gain which is changedarbitrarily at high speed, such as a pulse-like image pick-up gain to beused for releasing a shutter for only a short period of time or anincrement or decrement image pick-up gain, can be achieved.

In a case where the image pick-up section 11 is used in each of theprevious embodiments, the image pick-up section 11 must acquire an imagetwice for calculating R₊, R⁻, or R and output a video signal pertainingto two screens per frame while the signal is split. To this end, in theimage pick-up section 11, the image pick-up element 6 is activated twiceas fast as it is activated in normal times, to thereby acquire a videosignal pertaining to two images. The video signal is output from theimage split circuit 22 while being divided into a video signal S41 and avideo signal S42. Alternatively, so long as there is employed an imagepick-up element capable of acquiring an image for each pixel and atevery image pick-up operation while effecting switching between thevideo signal S41 and the video signal S42, the video signals 41 and 42can be output while they are split.

As mentioned above, the image pick-up section 11 whose configuration isshown in FIG. 10 can be used as means for controlling the image pick-upgain under the three-dimensional information detecting method of thepresent invention. Further, the image pick-up section 11 can also beused as means for outputting two video signals resulting fromtwice-acquisition of an image while being split.

FIG. 11 shows a signal processing section 7 which is an embodiment ofthe signal processing section 7 shown in FIG. 1. In this signalprocessing section 7, an internal signal is driven at a rate—which isthe same as the number of pixels of the video signal—and is subjected topipe-line processing in individual circuits. After a synchronous signalhas been eliminated from the video signals S41 in a synchronous signalseparation circuit 41, the video signal S43 is stored in an imagepick-up level storage circuit 1, and the video signal S44 is stored inan image pick-up level storage circuit 2. A signal S45 output from theimage pick-up level storage circuit 1 and a signal S46 output from theimage pick-up level storage circuit 2 are input to a computation circuit44, where R₊, R⁻, or R and the distance “d” are computed. A signal S47output from the computation circuit 44 is a time-series signal resultingfrom two-dimensional scanning of the distance between the respectivesections of the object. Time-axis fluctuations in the signal S47 arecorrected by a storage circuit 45, and a synchronous signal is added tothe thus-corrected signal b a synchronous signal addition circuit 46.The signal is output as a three-dimensional signal S5 whose video levelcorresponds to the value of information pertaining to the distance “d”between the respective points of the object. As mentioned above, thesignal processing section 7 whose configuration is shown in FIG. 11 canbe used as a means for computing three-dimensional informationpertaining to an object in real time under the three-dimensionalinformation detecting method of the present invention.

Advantageous Result of the Invention

As has been described in detail, the present invention enablestwo-dimensional determination of the distance between individual pointsof an object at a speed at which the three-dimensional information canbe followed real time within a period of time corresponding to the frameof a video signal, as well as detection of three-dimensionalinformation, by utilization of information pertaining to the intensityof an image of the object acquired under condition that either theintensity of illumination light or an image pick-up gain is changed withtime. Consequently, the method and apparatus of the present inventioncan be suitably used for acquiring a three-dimensional motion picture ofan object.

1. A method of detecting three-dimensional information, comprising:illuminating an object with an illumination light; acquiring an image ofthe object illuminated by the illumination light by acquisition of atleast two image pick-up gain, at least one of said image pick-up gainchanging with time, and the image pick-up gain having slower changingrate than a changing rate of the illumination light, wherein the imageis acquired a plurality of times by an image pick-up element havingstorage effect; and detecting a distance between individual points ofthe object on the basis of the image obtained; wherein the distancebetween respective points of the object is detected at a speed at whichthree-dimensional information is followed real time within a period oftime corresponding to a frame of a video signal.
 2. The method ofdetecting three-dimensional information as defined in claim 1, whereinthe first image pick-up gain changes with time, and the second imagepick-up gain is uniform.
 3. The method of detecting three-dimensionalinformation as defined in claim 1, wherein the first image pick-up gainis increased with time, and the second image pick-up gain is decreasedwith time.
 4. A method of detecting three-dimensional information,comprising: illuminating an object with an illumination light; acquiringan image of the object illuminated by the illumination light byacquisition of at least two image pick-up gain, at least one of saidimage pick-up gain changing with time, and the image pick-up gain havingslower changing cycle than a illuminating time of the illumination lightwith given level of intensity, wherein the image of the object isacquired a plurality of times by an image pick-up element having storageeffect; and detecting a distance between individual points of the objecton the basis of the image obtained; wherein the distance betweenrespective points of the object is detected at a speed at whichthree-dimensional information is followed real time within a period oftime corresponding to a frame of a video signal.
 5. The method ofdetecting three-dimensional information as defined in claim 4, whereinthe first image pick-up gain changes with time, and the second imagepick-up gain is uniform.
 6. The method of detecting three-dimensionalinformation as defined in claim 4, wherein the first image pick-up gainis increased with time, and the second image pick-up gain is decreasedwith time.
 7. A method of detecting three-dimensional information,comprising: illuminating an object with an illumination light acquiringan image of the object illuminated by the illumination light byacquisition of at least two image pick-up gain, at least one of saidimage pick-up gain changing with time, and the image pick-up gain havingslower changing rate than a changing rate of the illumination light,wherein the image is acquired a plurality of times by an image pick-upelement having storage effect; and detecting a distance betweenindividual points of the object on the basis of the image obtained;wherein the distance between respective points of the object is detectedat a speed at which three-dimensional information is followed real timewithin a period of time corresponding to a frame of a video signal,wherein first and second optical images of the object illuminated byfirst and second illumination light which illuminate with singleintensity over a predetermined period of time, are formed; first andsecond images are obtained alternately by acquiring the first and secondoptical images with first and second image pick-up gains, the first andsecond images obtained are stored; and the distance between respectivepoints of the object is detected from the first and second images whichare detected sequentially for each frame of the video signal.
 8. Amethod of detecting three-dimensional information, comprising:illuminating an object with an illumination light; acquiring an image ofthe object illuminated by the illumination light by acquisition of atleast two image pick-up gain, at least one of said image pick-up gainchanging with time, and the image pick-up gain having slower changingcycle than a illuminating time of the illumination light with givenlevel of intensity, wherein the image of the object is acquired aplurality of times by an image pick-up element having storage effect;and detecting a distance between individual points of the object on thebasis of the image obtained; wherein the distance between respectivepoints of the object is detected at a speed at which three-dimensionalinformation is followed real time within a period of time correspondingto a frame of a video signal, wherein first and second optical images ofthe object illuminated by first and second illumination light whichilluminate with single intensity over a predetermined period of time,are formed; first and second images are obtained alternately byacquiring the first and second optical images with first and secondimage pick-up gains, the first and second images obtained are stored;and the distance between respective points of the object is detectedfrom the first and second images which are detected sequentially foreach frame of the video signal.